1. Field of the Invention
The present invention relates generally to the field of data collection, and in particular to a new and useful method for achieving full matrix capture and processing of waveform data by employing an ultrasound array apparatus.
2. Description of the Related Art
In ultrasonic testing, very short ultrasonic pulse-waves with center frequencies ranging typically from 0.1 to 15 MHz and, occasionally, up to 50 MHz are launched into materials to detect internal flaws or to characterize materials. The technique is also commonly used to determine the thickness of a tested object, for example, to monitor pipe wall corrosion.
Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with lower resolution. It is a form of non-destructive testing used in many industries.
Two basic methods of receiving the ultrasound waveform are pulse-echo and pitch-catch. In pulse-echo mode the transducer performs both the sending and the receiving of the pulsed waves as the “sound” is reflected back to the device. The reflected ultrasound comes from an interface such as the back wall of the object or from an imperfection within the object. The diagnostic machine typically displays these results in the form of a signal with amplitude representing intensity of the reflection and arrival time of the reflection representing distance. In pitch-catch mode separate transducers are employed to transmit and receive the ultrasound.
There are a number of benefits to ultrasound testing. This testing method provides high-penetrating power, which allows the detection of flaws deep in the part being analyzed. It is also a high sensitivity form of testing, permitting the detection of extremely small flaws. Generally only one surface needs to be accessible for ultrasound testing. The method provides greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces. It provides some capability of estimating the size, orientation, shape and nature of defects. It is generally nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity. It is also capable of portable as well as highly-automated operation.
One type of ultrasound testing is known as phased array ultrasound. For this type of testing the probe(s) are comprised of a plurality (array) of elements, each of which can transmit and/or receive ultrasound independently. By combining the transmitted waves from each individual element a composite sound beam is created. This beam may be steered and/or focused in an arbitrary manner by applying short time delays across the elements and then firing the elements together. In an analogous manner a receive array may be set to be sensitive to incoming ultrasound from a particular angle and/or focal depth by applying a set of short delays across elements and subsequently adding together contributions from all elements.
Matrix capture of ultrasonic information is a powerful technique for inspection which uses the same array probes as phased array ultrasound. The method is distinct, however. Matrix capture is achieved, for example, by firing each array element in succession and recording the received waveforms at all elements for each firing. The resulting collected data at a given inspection location forms a matrix of waveforms for which each waveform is associated with one transmit-receive element pair. By acquiring all data for every transmit/receive element pair over the array, virtual ultrasonic scans at arbitrary angles can be reconstructed at any time after data has been collected by applying the appropriate set of short delays to the recorded waveforms and then adding all signals together (using a computer, for instance).
Matrix capture is identified as distinct from phased array in the following manner. In the phased array method, at a given inspection location the appropriate set of short delays is applied to all waveforms during transmit and receive phases, and at that time waveforms from all array elements are summed together. Only the final result is stored. In the matrix capture method all waveforms corresponding to every combination of transmit and receive element at each inspection location are stored in a data matrix. At any subsequent time in post-processing the appropriate set of short delays are applied to the stored waveforms and all waveforms in the matrix are summed together in order to effectively create a steered and/or focused beam of ultrasound.
Known matrix capture techniques, however, have an inherent and significant disadvantage, namely the need for storing a large amount of data. All waveforms for all transmit/receive pairs must be stored for every scan location.
By way of an illustration, each waveform typically requires 1000 time points to be collected, each point requiring one byte. For a 32-element array this means that (32)2, or 1024, waveforms must be collected. At 1000 bytes each, this collection results in 1 MB of data stored for each scan location. Even a small scan will require on the order of 100 times 100, or 10,000, scan locations. This collection of data will result in total data storage of about 10 GB. For the case of a pulse-echo inspection with a probe containing m elements the number of waveforms that must be collected per scan location, including reciprocity considerations, is:
      Number    ⁢                  ⁢    of    ⁢                  ⁢    waveforms    ⁢                  ⁢    per    ⁢                  ⁢    inspection    ⁢                  ⁢    location    ⁢                  ⁢          (              pulse        ⁢                  -                ⁢        echo            )        =                    m        ·                  (                      m            +            1                    )                    2        .  This requirement strains data storage needs, and also can place a practical limitation on scan speed because it can be difficult to rapidly move so much data.
Gains in efficiency can be realized by a method in which scan and/or index increments are set equal to element pitch or unit fractions thereof. In this case a large fraction of the collected data at one location is (theoretically) identical with data collected at neighboring locations.
One illustrative example involves a situation in which the array probe is operating in pulse-echo mode and has three elements. The probe will be moved to three separate positions along the same direction as the ultrasonic array. At any given position, in order to accumulate data from all transmit-receive pairs with a standard method of data capture then
            m      ·              (                  m          +          1                )              2    =                    3        ·        4            2        =    6  waveforms must be recorded. Additionally, each of the three elements must be fired once. In order to collect all data for the three probe positions a total of 9 element firings are needed and 18 waveforms must be collected.
This situation is illustrated in FIG. 1, in the section marked “Standard Data Collection.” A set of tables are shown, each representing the data matrices for a probe at subsequent inspection locations (shown in the upper left) corresponding to a 3-element array moving in increments of one element pitch. Tables from left to right represent data matrices which need to be filled in each subsequent location (A, B, C). Tables from top to bottom represent these same arrays at subsequent probe locations (A, B, C). The data required at each location is a set of waveforms corresponding to each transmit-receive pair. The letters in the tables represent the probe location at which data is collected. For standard collection, at each probe location (A, B, and C), all data for reconstruction at that respective location is collected.
In the case where the probe is moved along the array direction at a step size equal to the element pitch, if the elements are fired 9 times and 18 waveforms are collected then much of the data is redundant.
Thus, a need exists for a method of capture of waveform data that is efficient and overcomes the above deficiencies, including, but not limited to, redundancies and strain on storage capacity.